U.S. patent application number 13/459679 was filed with the patent office on 2012-11-08 for pressure sensitive adhesive for application on skin and process for the production thereof.
This patent application is currently assigned to ADHESIVES RESEARCH, INC.. Invention is credited to Ranjit MALIK, Kevin MCKINNEY.
Application Number | 20120283615 13/459679 |
Document ID | / |
Family ID | 46086058 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120283615 |
Kind Code |
A1 |
MALIK; Ranjit ; et
al. |
November 8, 2012 |
PRESSURE SENSITIVE ADHESIVE FOR APPLICATION ON SKIN AND PROCESS FOR
THE PRODUCTION THEREOF
Abstract
Pressure sensitive adhesives for use primarily in medical
applications are disclosed. The pressure sensitive adhesives are
urethane elastomeric adhesives that include a polyurethane polymer
and a compatible tackifier and/or compatible plasticizer to achieve
an adhesive having a predetermined compliance. The result is a
pressure sensitive adhesive for application to skin that can
eventually be removed with very little trauma to the skin and with
a low pain rating, but which still exhibits very good peel strength
when used to construct an article in which the adhesive is adhered
to human skin.
Inventors: |
MALIK; Ranjit; (York,
PA) ; MCKINNEY; Kevin; (Glen Rock, PA) |
Assignee: |
ADHESIVES RESEARCH, INC.
Glen Rock
PA
|
Family ID: |
46086058 |
Appl. No.: |
13/459679 |
Filed: |
April 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61481948 |
May 3, 2011 |
|
|
|
Current U.S.
Class: |
602/52 ; 523/111;
602/54 |
Current CPC
Class: |
A61L 15/58 20130101;
C08G 2170/40 20130101; C09J 175/16 20130101; C09J 7/22 20180101;
C09J 2475/00 20130101; A61L 15/58 20130101; C08K 5/103 20130101;
C08K 5/0016 20130101; C09J 2475/006 20130101; C08K 2201/014
20130101; C08L 75/04 20130101; C09J 7/38 20180101 |
Class at
Publication: |
602/52 ; 602/54;
523/111 |
International
Class: |
A61F 13/02 20060101
A61F013/02 |
Claims
1. A medical pressure sensitive adhesive comprising a polyurethane
elastomer and a plasticizer, tackifier, or both, wherein the
adhesive has compliance properties corresponding to a TA Peak Force
in the range of 40 grams to 180 grams and a percent loss in the
range of 40% to 95%.
2. The adhesive of claim 1, wherein the polyurethane elastomer is
comprised of a plurality of urethane linkages and is substantially
free of isocyanate functionality.
3. The adhesive of claim 1, wherein the polyurethane elastomer has
a weight average molecular weight of greater than 25,000 g/mol.
4. The adhesive of claim 1, wherein the polyurethane elastomer has
a weight average molecular weight in the range of 50,000 g/mol to
150,000 g/mol.
5. The adhesive of claim 1, comprising about 10% to about 60% by
weight plasticizer.
6. The adhesive of claim 1, wherein the polyurethane elastomer and
plasticizer are biocompatible.
7. An article comprising a substrate and a medical pressure
sensitive adhesive laminated to the substrate, the adhesive
comprising a polyurethane elastomer and a plasticizer, tackifier,
or both, wherein the adhesive has compliance properties
corresponding to a TA Peak Force in the range of 40 grams to 180
grams and a percent loss in the range of 40% to 95%.
8. The article of claim 7, wherein the adhesive has a thickness in
the range of about 20 to about 100 microns.
9. The article of claim 7, wherein the article has a stripping
effect of a maximum of 20% when the adhesive is applied to human
skin.
10. The article of claim 7, wherein the average pain rating upon
removal of the adhesive from human skin is less than 2.5 on the
Wong Baker pain scale.
11. The article of claim 7, wherein the adhesive exhibits a
moisture vapor transmission rate value of greater than 1000
g/m.sup.2-day.
12. The article of claim 7, wherein the article is a wound
dressing.
13. The article of claim 12, wherein the substrate is a
polyurethane film.
14. The article of claim 7, wherein the article exhibits edge lift
of less than 5% after 24 hours when applied to human skin.
15. The article of claim 7, wherein the adhesive has a peel
strength of greater than 0.8 N/cm after 24 hours when applied to
human skin.
16. A medical article comprising a substrate; a pressure sensitive
adhesive having a thickness of about 25 to about 50 microns
laminated to the substrate, the pressure sensitive adhesive
comprising a polyurethane elastomer and a plasticizer, the adhesive
having compliance properties corresponding to a TA Peak Force in
the range of 40 grams to 180 grams and a percent loss in the range
of 40% to 95%, wherein the article has a stripping effect of a
maximum of 20% when the adhesive is applied to human skin, the
average pain rating upon removal of the adhesive from human skin is
less than 2.5 on the Wong Baker pain scale, the adhesive exhibits a
moisture vapor transmission rate value of greater than 1000
g/m.sup.2-day, the article exhibits edge lift of less than 5% after
24 hours when applied to human skin, and the adhesive has a peel
strength of greater than 0.8 N/cm after 24 when applied to human
skin.
17. A method of manufacturing a medical pressure sensitive adhesive
comprising: providing a polyurethane elastomer base pressure
sensitive adhesive; and modifying the adhesive with a plasticizer,
tackifier, or both, to achieve compliance properties of the
adhesive corresponding to a TA Peak Force in the range of 40 grams
to 180 grams and a percent loss in the range of 40% to 95%.
Description
RELATED APPLICATION
[0001] This application claims the benefit of and priority to U.S.
Provisional Application No. 61/481,948, filed May 3, 2011, which is
hereby incorporated by reference in its entirety.
FIELD
[0002] The present application is directed toward the field of
pressure sensitive adhesive compositions and their production and
more particularly to such compositions adapted for medical
applications such as wound care and the like.
BACKGROUND
[0003] Most pressure sensitive adhesives currently used in
connection with dressings for skin and wound-care bond tenaciously
to the skin. The level of bond strength builds up even after just a
few hours of wear. The sensory perception felt when peeling back
such adhesives that have had even just a few hours to dwell on the
skin is typically quite painful and causes damage to the epidermal
layer of the skin. Pain can be caused by trauma to the skin by way
of induced edema and/or erythema.
[0004] Furthermore, dressings are often used to repeatedly cover
the same site of the body, resulting in repeated removal and
reapplication of the adhesive. When repeatedly applied and removed,
such adhesives are apt to remove with them parts of the upper skin
and cause damage to the skin. The damage to the skin can manifest
in an increase in transdermal water loss. These adhesives also
fasten strongly to hair on the skin, which adds to the discomfort
and irritation experienced when the adhesive is removed.
Additionally, the skin layer stripped by the adhesive during
removal deadens the tack and the adhesive properties, thus
diminishing the reapplication potential of the adhesive.
[0005] Gel adhesives provide an alternative to pressure-sensitive
adhesives and are more gentle to the skin. A gel adhesive has a low
peel with skin and can be removed with little damage and it
typically wets out the surface well. However, gel adhesives have
shown poor adhesive performance because the tape or dressing easily
gets caught on clothing or other surfaces and rolls off. The
adhesive bond does not have the strength to overcome the rolling
action. Once the edge of the adhesive rolls, it readily picks up
lint and other debris that will prevent it from re-bonding to the
skin and eventually the product will fail. Additionally, the edge
roll can lead to contamination of the healing site. As a result,
gel adhesives do not have sufficient wear properties for most wound
care applications. Common gel adhesives include silicone and
polyurethane gels, although most of the polymers for polyurethane
gel adhesives are made using catalysts that render the adhesive
cytotoxic and, as a result, are not suitable for application on
skin.
[0006] Silicone gel adhesives are sometimes used in wound
applications, since most do not have cytotoxicity concerns.
However, these adhesives still do not bond well to the skin if the
adhesive thickness is less than 80 microns, and typically up to 150
microns. Yet while the initial bond to the skin improves with
increasing thickness, the overall wear properties are not improved
due to edge lift resulting from the larger exposed adhesive area at
the edge of the dressing. This exposed adhesive edge tends to
"grab" clothing, bedding or other contacted materials which then
results in the edge lifting. In the worst case, edge lift results
in rolling of the dressing to the point of complete removal. Yet
another drawback is that the cost of silicone gels is substantially
higher than other commercially available adhesives. Furthermore,
ionizing radiation, often used for sterilization of wound
dressings, can have a particularly detrimental effect on silicone
gel adhesives, resulting in much lower bonds to the skin. For this
reason, silicone gel adhesives are usually sterilized using an
ethylene oxide sterilization procedure, a more expensive process
that further contributes to higher manufacturing costs.
[0007] In order to address the desire for pain free removal, the
concept of adhesive inactivation has also been discussed in the
literature. Acrylic, polyurethane or rubber based adhesives may be
used in conjunction with the deactivation method. The deactivatable
adhesive can form strong bonds until it is time for removal. Using
a trigger mechanism, at the time of removal, the adhesive is made
to lose its bond strength. Various trigger mechanisms, such as
light source, use of saline solution, and the use of microcapsules
filled with oils have been proposed. A common drawback with any of
the inactivation methods is that it is irreversible. Once
inactivated the adhesive permanently loses its adhesive properties.
The capability to reapply the adhesive is lost. Further
disadvantage of adhesives that deactivate with light source is that
these cannot withstand gamma or e-beam sterilization methods.
Deactivation with the microcapsule method relies upon rupturing of
microcapsules with application of pressure to the adhesive followed
by migration of oil in the adhesive. Oil migration is a slow
process. Further, it is extremely difficult to standardize the
pressure for individual patients and inadvertent inactivation of
the adhesive cannot be prevented. This is further complicated
because applying pressure to a wound is not desirable.
[0008] Hydrogels and hydrocolloids can also be formulated to
provide a more gentle adhesive, however the adhesive properties of
these materials change dramatically as they absorb or lose water
from/to the environment or wound site, often resulting in
adhesive/skin bond failure. Hydrogels and hydrocolloids are also
applied as thick layers of greater than 80 microns due to their
weak bonds to the skin at lower adhesive thicknesses.
[0009] Yet another drawback of silicone, rubber, and acrylic-based
pressure sensitive adhesives currently used with wound care is that
these adhesives generally have poor moisture vapor transmission
rate (MVTR) performance. In order to improve the MVTR in wound-care
dressings for these types of adhesives, one or more of the
following measures is typically taken: the adhesive is coated as a
very thin layer, generally less than 30 microns; the adhesive is
pattern coated on the web to create a substantial adhesive-free
area to allow for moisture transmission; the adhesive is coated to
form a porous or microporous structure so that the skin can
breathe; and/or the adhesive is perforated to create an
adhesive-free area.
[0010] The use of a low coating thickness can be inconsistent with
achieving a threshold adhesive mass for good bond formation, while
pattern coating, formation of pores, and perforation may
necessitate additional process steps in manufacture, which can
increase manufacturing costs. Furthermore, in some cases, the
presence of pores and holes may be undesirable as they may allow
ingress of bacteria into the wound. In some cases, the adhesive
free areas resulting from pattern coatings may compromise wear
performance.
[0011] Accordingly, there is a need in the medical and wound care
marketplace for an adhesive that can be removed from the skin with
little or no pain and for such an adhesive that also exhibits
suitable wear performance. There is a further need for adhesives
that have the ability to be repositioned on the skin if the
adhesive were misapplied in the initial application as well as
reapplied after removal for wound inspection. There is still a
further need to provide such adhesives that can be manufactured and
sold in a cost effective manner. There is also a need for an
adhesive that retains performance characteristics upon gamma
sterilization. There is also a need for an adhesive that has high
MVTR characteristics.
SUMMARY
[0012] Exemplary embodiments of the present invention provide a
pressure sensitive adhesive that address these and other
deficiencies currently found in the art. The PSA can be used in
fabricating medical devices such as affixing tapes, wound
dressings, and other articles in contact with human skin.
[0013] According to one embodiment, a medical pressure sensitive
adhesive is provided that comprises a polyurethane elastomer and a
plasticizer or tackifier, wherein the adhesive has compliance
properties corresponding to a TA Peak Force in the range of 40
grams to 180 grams and a percent loss in the range of 40% to
95%.
[0014] According to another embodiment, an article comprises a
substrate and a medical pressure sensitive adhesive laminated to
the substrate, the adhesive comprising a polyurethane elastomer and
a plasticizer or tackifier, wherein the adhesive has compliance
properties corresponding to a TA Peak Force in the range of 40
grams to 180 grams and a percent loss in the range of 40% to
95%.
[0015] In certain embodiments, the article has a stripping effect
of a maximum of 20% when the adhesive is applied to human skin. In
certain embodiments, the average pain rating upon removal of the
adhesive from human skin is less than 2.5 on the Wong Baker pain
scale. In certain embodiments, the adhesive exhibits a moisture
vapor transmission rate value of greater than 1000 g/m.sup.2-day.
In certain embodiments, the article exhibits edge lift of less than
5% after 24 hours when applied to human skin. In certain
embodiments, the adhesive has a peel strength of greater than 0.8
N/cm after 24 when applied to human skin. In preferred embodiments,
all of these properties are exhibited.
[0016] An advantage of exemplary embodiments is that a pressure
sensitive adhesive is provided for use in medical applications that
has sufficient adhesive strength to hold a dressing or other
article in place but that can be removed with very little trauma to
the skin or corresponding pain to the patient.
[0017] Another advantage is that the adhesive permits a dressing or
other medical article to which it is applied to be removed and
subsequently re-attached without relevant loss in adhesive
strength.
[0018] Still another advantage is that the adhesive does not
exhibit a loss of tack such that if a bandage or other medical
article is misapplied or folds over during application, it can be
reworked and applied correctly without the need to obtain a new
bandage.
[0019] Other features and advantages of the present invention will
be apparent from the following more detailed description of
exemplary embodiments, which illustrate, by way of example, the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1 and 2 are a side and top view, respectively, of a
medical article employing an adhesive in accordance with an
exemplary embodiment.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0021] Pressure sensitive adhesives in accordance with exemplary
embodiments are urethane elastomeric adhesives that comprise a
polyurethane polymer and a compatible tackifier and/or compatible
plasticizer to achieve an adhesive having a predetermined
compliance. In some embodiments, the adhesive is then coated on a
substrate, followed by subsequent drying/curing by passing it
through a hot air oven or alternatively under UV light. The
resulting product is a pressure sensitive adhesive for application
to skin that can eventually be removed with very little trauma to
the skin and with a low pain rating.
[0022] Exemplary embodiments are thus directed to a urethane
elastomeric pressure sensitive adhesive that can be removed from
the skin with little to no pain and with little or no trauma to
skin but which also can easily be reapplied or repositioned and
resists edge rolling when used in conjunction with a tape,
dressing, or other article. The polyurethane pressure sensitive
adhesives in accordance with exemplary embodiments provide the
ability to lift-up a dressing for inspection of a wound and then to
re-attach the adhesive without relevant loss in adhesive strength,
which is highly advantageous in a clinical setting. This also
allows a clinician to rework the adhesive patch in case it is
misapplied or folds over on itself. This simplifies handling and
also saves time for clinical staff.
[0023] Accordingly, exemplary embodiments are further directed to
the use of urethane elastomeric pressure sensitive adhesives in
connection with medical applications such as wound care, incise
drapes, securing intravenous sites, and vacuum assisted closure and
the present invention also relates to a wound dressing, affixing
tape or other medical device for skin application that includes a
substrate coated on at least one side with the adhesives described
herein. In addition to wound dressings and affixing tapes, the
urethane elastomeric pressure sensitive adhesives can be used in
fabricating medical devices such as medical drapes, IV site
dressings, surgical gowns and drapes, transdermal delivery systems,
medical device fixation, and other medical devices for attaching to
the skin, all by way of example only.
[0024] Exemplary embodiments provide adhesives in which the pain
experienced on removal is low, even after up to 5 days of wear; the
adhesion does not significantly build with time; the adhesive has a
MVTR in excess of 1000 g/m.sup.2 per day; does not cause maceration
of the skin; and the surface of the adhesive is substantially free
of skin cells when the adhesive is peeled back.
[0025] The base polymer for pressure sensitive adhesives in
accordance with exemplary embodiments is a polyurethane. The
polyurethane may be any suitable biocompatible, hydrophilic
polyurethane which can be modified such that the formulated
urethane elastomer pressure sensitive adhesive exhibits a
compliance having a TA Peak Force in the range of 40 grams to about
180 grams and a percent loss in the range of 40% to 95%, as
described in more detail herein. Conventional PSAs used as medical
adhesives have a TA Peak Force in the range of 200 to 500 grams.
The inventors unexpectedly discovered that PSAs that exhibit a TA
Peak Force of 180 grams or less result in the pain sensation on
skin being greatly diminished. The compliant urethane elastomer
adhesives used in accordance with exemplary embodiments have weaker
adhesive bonds to the skin than the pressure sensitive adhesives
normally used for adhesive dressings. Consequently, these
elastomers leave the stratum corneum essentially intact when
dressings containing these elastomers are peeled or pulled away
from the skin.
[0026] In one embodiment, the polyurethane is comprised of a
plurality of urethane linkages and is substantially free of
isocyanate functionality (i.e., in which no NCO content is detected
by FTIR spectroscopy). The polyurethane typically has a weight
average molecular weight in excess of 25,000 g/mol, preferably
between 50,000 and 150,000 g/mol. The polyurethane is further
selected to be soft and elastomeric, but with high strength. The
glass transition temperature of the polyurethane is preferably less
than -25.degree. C. and the compliance can be readily modified.
Furthermore, the polyurethane should not absorb water but be
capable of transporting large amounts of moisture.
[0027] The polyurethane may be formed through polymerization of
commercially available polyurethane resins with terminal acrylic
functionality or mixtures thereof, including those available from
Bomar Specialties as BR-3641AA, BR-3731, and BR-3741AB or any one
of CN3211, CN9004, CN9018, CN9290US, or CN9782, available from
Sartomer, by way of example only. Alternatively, the polyurethane
may be obtained as a pre-polymerized PSA solution. Exemplary such
polymers include the polyurethane-based pressure-sensitive adhesive
available as Cyabine SP-205 produced by Toyo Ink Mfg. Co., Ltd.,
again by way of example only. In still other embodiments, the
polyurethane can be obtained by the reaction of an isocyanate
terminated resin with a hydroxyl terminated resin. Exemplary
materials include reacting isocyanate resins such as Mondur and
Desmodur available from Bayer with polyols such as Acclaim, Arcol,
Desmophen, or Multranol, all of which are also available from
Bayer.
[0028] Exemplary adhesive formulations further include a tackifier
and/or plasticizer. The plasticizer is selected for its
biocompatibility and its ability to modify the compliance of the
adhesive formulation and to achieve the other properties described
herein. The plasticizer should be non-volatile and be insoluble in
water and should also not absorb water or other bodily fluids. The
adhesive formulation is typically about 10% by weight to about 60%
by weight plasticizer, and in some cases may be in the range of
about 20% by weight to about 55% by weight plasticizer. In some
embodiments, the plasticizer may be present in the range of about
30% to about 40% by weight.
[0029] The plasticizer is selected to be compatible with
polyurethane across a range of loading levels, forming a single
phase and exhibiting little or no sweating out with increasing time
and/or temperature. Furthermore, it should be selected such that
the resulting formulated adhesive does not leave residue on the
skin upon removal. It will thus be appreciated that the selection
of a particular plasticizer may depend upon the particular
polyurethane elastomer used as the base component of the PSA.
[0030] Suitable plasticizers may include triisodecyl trimellitate;
tributyl trimellitate; tri-n-hexyl trimellitate; tris
n-(C7-11)alkyl ester branched and linear 1,2,4 benzenetricarboxylic
acid; butyl benzoate; di-ethylhexylphthalate; di-octylphthalate;
di-butylphthalate; diethylhexyl adipate; dibutyl adipate; triethyl
citrate; tributyl citrate; acetyl triethyl citrate; acetyl
trin-butyl citrate; n-butyryl tri-n-hexyl citrate; triacetin;
glycerin; caprylic/capric triglyceride; tricaprin; tricaprylin;
propylene glycol dicaprate; propylene glycol dicaprylate/dicaprate;
poly(ethylene glycol) (PEG); hydrogenated vegetable oil;
hydrogenated seed oil; PEG dilaurate; PEG diethylhexylonate; and
combinations thereof.
[0031] Exemplary adhesive formulations further may include up to
about 50% by weight of a tackifier. The tackifier may be selected
from the group consisting of rosin esters, polymerized rosins,
hydrogenated rosins, polyterpenes, styrenated terpenes, polymerized
hydrocarbon resins, alpha methyl styrenes, alpha methyl styrene
phenolics and combinations thereof. Exemplary tackifiers include
those which are commercially available as Escorez 1310, Sylvares
SA120, Sylvares TP105, Foral 85, and Sylvares 540. As with the
plasticizer, the tackifier is selected for its biocompatibility
(i.e., its ability to be safely in contact with the skin and/or
bodily fluids) and compatibility with (i.e., its ability to form a
single phase with) the polyurethane resin.
[0032] Despite the presence of plasticizers and tackifiers, which
are relatively small molecules compared to the base polymer,
exemplary embodiments exhibit little to no migration of the
plasticizer or tackifiers from the adhesive because of their
compatibility with the polyurethane polymer, having closely matched
solubility parameters and being completely miscible in one another
over an expected temperature range of adhesive storage and use.
[0033] Exemplary embodiments may also employ a cross-linking agent.
The cross-linking agent may be present up to about 5% by weight of
the polyurethane on a solids basis, more typically up to about 3%
by weight of the polyurethane on a solids basis, and in some cases
in the range of about 0.75% to about 2.25% by weight of the
polyurethane on a solids basis. Any suitable cross-linking agent
may be used, including isocyanates and aziridines, and metal
chelates such as Tyzor TBT, and Tyzor GBA (both available from
Dupont), by way of example only.
[0034] Other additives in the types and amounts as are known in the
art for use in conventional pressure-sensitive adhesives may also
be employed, provided those additives do not adversely affect the
properties otherwise sought to be achieved. Such additives may
include antioxidants, stabilizing agents for enhanced shelf-life,
and the like. Agents added to stabilize the adhesive against the
detrimental effects of gamma sterilization include, but are not
limited to, those commercially available as Irganox 1010, Irganox
1076, Irganox 245, Irganox 3052F, Irganox E201, Irganox B225,
Ubiquinone, Tinuvin 662, and Tinuvin 770.
[0035] Pressure sensitive adhesives in accordance with exemplary
embodiments used to affix materials to the body are compatible with
skin. Biocompatibility of pressure sensitive adhesives is
characterized by cytotoxicity, skin irritation, and skin
sensitization. The cytotoxicity of adhesives in accordance with
exemplary embodiments does not exceed 2 when using the ISO agrose
overlay method; preferably the cytotoxicity is less than 1 and most
preferably is zero. The skin irritation, using the ISO skin
irritation rating, does not exceed 2 and preferably is less than or
equal to 0.4 (non-irritating). Adhesives in accordance with
exemplary embodiments do not act as skin sensitizers under Globally
Harmonized System for Classification and Labeling of Chemicals
(GHS) standards.
[0036] Exemplary embodiments result in adhesive compositions that
can be applied to skin, such as in conjunction with the application
of a dressing, affixing tape, or other medical device adhered to
the skin and that can be subsequently removed with little or no
pain. Although pain experienced during adhesive removal can be
difficult to measure precisely as it can be influenced by a wide
range of factors, the Wong-Baker pain scale is recognized in the
medical field to quantify pain intensity measurement. This 0 to 5
scale, with 5 being the highest pain level, is often used to gauge
the pain experience of an individual. Exemplary embodiments achieve
an average Wong-Baker pain rating of less than 2.5 during adhesive
removal even after up to 5 days of wear, typically less than 2.0,
preferably less than 1.5, and in some cases less than 1.0.
[0037] The inventors have found that polyurethane based pressure
sensitive adhesives falling within a specified compliance range are
much gentler on the skin, while meeting the desired wear
performance. Surprisingly, the inventors have further determined
that the peel strength of the adhesive does not correlate with
pain. Observation of the bond failure mechanism of conventional
adhesives suggest that the bond failure when peeling the adhesive
from skin does not take place at the adhesive-skin interface but
instead the failure takes place at the interface between the upper
layer of skin cells and the dermis. This is signified by the large
quantity of skin cells fouling the peeled-back adhesive. Therefore,
the force required to remove the adhesive from the skin is
essentially the same as the force at which the adhesive pulls off
large amounts of skin cells from the dermis layer (i.e., resulting
in trauma to the skin and thus translating to pain felt by the
wearer).
[0038] In the inventive adhesive the bond failure occurs at the
adhesive-skin interface which is signified by none or very little
skin cell fouling the adhesive. Using this underlying difference in
the mechanism of bond failure when peeling from skin, the inventors
were able to develop a unique system that possesses both high peel
and low pain upon removal. Put yet another way, while the terms
low-peel, low-trauma and low pain have generally been used
interchangeably in the art, the inventors have determined that this
usage is incorrect. Thus, while two adhesives could exhibit similar
peel force, they may be very different in the pain experienced by
the individual. It will be appreciated that the amount of skin
cells removed during peeling may be very different for different
adhesives despite a similar peel value. The higher the amount of
skin cells removed, the higher the pain experienced during the
removal.
[0039] Adhesives in accordance with exemplary embodiments have a
stripping effect of less than 50%, i.e. are capable of being
removed from the skin with less than 50% of the adhesive area being
fouled by detached skin cells and typically the stripping effect is
less than about 20%. In preferred embodiments, the stripping effect
is less than about 10%, such that up to 90% or more of the previous
bonding force is available so that the adhesive can be repositioned
and re-attached to the skin. Furthermore, the removal of fewer skin
cells correlates to less pain experienced by the wearer.
[0040] While it has been determined that peel force does not
correlate with pain, it does correlate with wear performance.
Exemplary embodiments also result in an adhesive that has suitable
wear performance. If the peel is reduced too much, then the
adhesive deteriorates in wear properties, i.e., tends to roll off
or fall off prematurely. Thus, the peel force is preferably as
close to, but not over, the amount of force required to remove a
majority of skin cells from the area of the skin in contact with
the adhesive, although it will be appreciated that force can vary
slightly from person to person, based on skin type, weather
conditions and diet, for example.
[0041] In order for the adhesive dressing or affixing tape for skin
applications to function effectively, the force with which the
compliant urethane elastomer adhesive adheres to the skin should
exceed the load to which it is subjected during normal use. The
peel force is on the order of 0.2 N force per centimeter of width
when peeling or stripping at an angle of 90.degree. from the skin.
Typically the force is more than 0.4 N/cm, which allows for the
vast majority of samples to bond to the skin for several days.
Preferably, the peel force is 0.6 N/cm using a 1 hour dwell and
over 0.8 N/cm after a 24 hour dwell on the skin.
[0042] One method of quantifying wear performance is edge lift.
Edge lift is a measure of the percentage of the total area of a
patch to which adhesive has been applied that is no longer bonded
to the skin during the wear-time. Exemplary embodiments achieve
less than 5% edge lift occurring over a 24 hour period.
[0043] Adhesives in accordance with exemplary embodiments also
exhibit high MVTR (greater than 1000 g/m.sup.2 day), an advantage
in medical applications which allows the skin to breathe. Adhesives
that do not breathe tend to accumulate moisture at the
skin-adhesive interface which in turn leads to maceration of the
skin. Macerated skin becomes weak and it can easily tear and cause
pain when the adhesive is removed. Accumulation of moisture also
promotes bacterial growth on the skin. A 25 micron thick layer of
adhesive in accordance with exemplary embodiments may exhibit an
MVTR of over 1500 g/m.sup.2 day, while even a 44 micron thick layer
of the adhesive coated on 25 micron polyurethane film can exhibit
an MVTR of 1400 g/m.sup.2 day.
[0044] Dressings and other devices making use of adhesives in
accordance with exemplary embodiments can also exhibit little or no
sliding or creep from the application site. They remove cleanly,
leaving little to no residue on skin or clothing, even if contacted
by fluids (e.g., water, isopropanol, wound exudate, etc).
[0045] Pressure sensitive adhesives in accordance with exemplary
embodiments are highly compliant while having high elongation
properties at break. The urethane elastomer pressure sensitive
adhesives exhibit a compliance having a peak force between the
range of about 40 to 180 grams and a percent loss in the range of
about 40 to 95%. Compliance is measured using a Texture Analyzer,
such as a TA-XT2i Texture Analyzer (available from Texture
Technologies Corporation) connected to a computer programmed with
the texture analyzer software. The method parameters for the test,
are outlined below in Table 1, the results of which are referred to
herein as the TA Peak Force.
TABLE-US-00001 TABLE 1 Parameter Definition Specification Mode The
type of test being run Force/Comp. Option The type of test sequence
being run Hold Until Time Distance The set height at which the
probe 50.0 mm resides prior to testing and after the test is
complete Pretest How fast the probe travels at the start of 4.00
mm/sec Speed the run until the trigger point is reached Trigger The
point at which a set minimal force 1.0 g Point is measured by the
load cell as the probe contacts the sample surface. When the
trigger force is reached, the test is started. Speed How fast the
probe travels after the 0.50 mm/sec trigger point through
compression to the designated force Time The amount of time that
the probe 140.00 sec resides on the sample surface after the force
has been achieved Post - Speed The speed at which the probe returns
8.00 mm/sec to the starting point where the test is finished Probe
The type of ball probe used for testing TA-8 1/4''
[0046] During sample preparation, liquid adhesive is direct coated
onto a siliconized liner and dried. The dried adhesive is then
layered onto a 50 micron thick polyester film until a thickness of
280.+-.25 micrometers has been achieved. During the test, the TA-8
probe (1/4'' ball probe) moves into contact with the surface of the
adhesive at a downward rate of 4.00 mm/second until a trigger force
of 1 gram is registered on the load cell. The adhesive layer is
then compressed to 50% of its total thickness at a rate of 0.50
millimeters/second which triggers data collection for the next 140
seconds. Throughout the entire test, the instrument continuously
measures the change in force over time. Data on force versus time
is generated into a graph on the computer. The initial peak force
is the force required to compress the adhesive layer to 50% of its
total thickness. The percent loss is related to the change in force
over time (i.e., the change in initial force to the final force
over the 140 second period of data collection).
[0047] Urethane elastomer pressure sensitive adhesives in
accordance with exemplary embodiments are formulated so that a TA
Peak Force between the range of about 40 to 180 grams and a percent
loss in the range about 40 to 95% is obtained. In some embodiments,
the TA Peak Force is between the range of 50 to 100 grams.
Typically the percent loss is in the range of 45 to 95%, more
typically in the range of 45% to 75% and preferably in the range of
50% to 65%. At TA Peak Force values greater than 180 grams, the
average pain experienced during removal increases beyond 2.0 on the
Wong-Baker scale. At a peak force less than 40 grams, the
polyurethane adhesive was so compliant that no peel force to the
skin could be measured (<0.1 N/cm), and the resultant wear
performance suffered. When the percent loss of the adhesives went
above 95% loss, the adhesive would leave a residue on the skin; at
values less than 40% loss, the adhesive is so cohesive it did not
satisfactorily wet out the skin surface and the material would fall
off during wear testing.
[0048] The strength of an adhesive bond can be quantified as a
mathematical product of two parameters: 1) the adhesive's ability
to make the bond and 2) the adhesive's resistance to break the
bond. Highest bond strengths are obtained when the adhesive easily
flows to conform to the substrate to form a bond and then resists
de-bonding by storing the de-bonding energy, achieving each of
these two parameters. Conversely, a restricted adhesive flow
prevents optimum contact with the substrate with respect to the
first parameter and if the adhesive is also highly dissipative, it
will not be in a position to resist debonding with respect to the
second parameter and this combination will result in poor bond
strength. The remaining combination of the two parameters will
result in intermediate bond strength (i.e., an easily conforming
adhesive that is also highly dissipative or an adhesive with
restricted flow but with high energy storage ability).
[0049] Without wishing to be bound by theory, the inventors believe
that exemplary embodiments of the invention having the compliance
characteristics set forth herein with respect to TA Peak Force and
percent loss correspond to a balance of the parameters that
provides the excellent combination of properties exhibited.
[0050] In any event, once formulated, adhesives in accordance with
exemplary embodiments may be coated as a continuous film onto a
carrier substrate using any one of the several methods known to
those skilled in the art for casting an adhesive film. The adhesive
may be applied to a thickness of about 20 microns to about 100
microns, typically in the range of about 25 microns to about 80
microns, more typically in the range of about 30 to about 50
microns. The adhesive may be applied as a continuous or a
discontinuous coating. The coating is subsequently dried/cured by
passing it through a hot air oven. Alternatively, the coating may
be exposed to UV radiation to affect curing. The adhesive film
and/or the dressing or other device to which it is applied may be
subjected to gamma radiation or other sterilization treatment
without an adverse effect on the adhesive or its properties.
[0051] As shown in FIGS. 1 and 2, adhesive 100 may be applied
directly to a substrate 200 to form a medical dressing 10 or other
device, or be formed as a single or double sided tape for use in
the later manufacture of a medical dressing or for direct use as an
affixing tape to secure the dressing. A siliconized or other
release liner 300 can be applied overlying the adhesive layer 100
to protect it prior to use.
[0052] In some embodiments, the substrate 200 to which the adhesive
is applied is a thin polymeric film, such as a polyurethane film.
These films are flexible and can follow the surface contours of the
skin. In still other embodiments, a support layer 400 of paper,
plastic or other suitable material may be used to improve
handleability of the polymeric film prior to its initial
application, which can then be peeled away.
EXAMPLES
[0053] The invention is further described by way of the following
examples, which are presented by way of illustration, not of
limitation.
Example 1
[0054] 43.06 grams (71.2% by weight) of an aliphatic urethane
acrylate oligomer (BR-3641AA from Bomar Specialties), 10.77 grams
(17.8% by weight) of 1,2,3-triacetoxypropane, 6.46 (10.7% by
weight) grams of cis-9-octadecen-1-ol, and 0.22 grams Irgacure 1700
(from Ciba) were mixed until homogeneous. The resulting mass was
then placed on 50 micron polyester film and 50 micron siliconized
polyester liner. The mass of adhesive between the films was then
pulled between 2 coating bars separated with a 350 micron feeler
gauge. The resulting adhesive mass was then cured with the films in
place using a 300 W/in UV lamp equipped with a H bulb using a
conveyor speed of 20 fpm. The sample was passed under the UV lamp
two times per side, 4 times total.
[0055] The adhesive was characterized by compliance according to
the TA Peak Force methodology described herein, yielding a peak
force of 54 grams, and a percent loss of 67%.
Example 2
[0056] 64.33 grams (50% by dry weight) of the polyurethane pressure
sensitive adhesive Cyabine SP-205 were blended with 0.53 grams of
Cyabine T-501B, 32.16 grams (50% by dry weight) of capric/caprylic
triglycerides, 0.141 grams Irganox 1010 and 1.13 grams of Irganox
3052FF to yield a clear solution. The resulting solution was coated
on a 30 micron polyurethane film by passing between coating bars
separated by a 300 micron feeler gauge. The resulting coating was
dried in an oven at 120.degree. C. for 5 minutes. The same coating
was also coated on 50 micron siliconized polyester liner using a
300 micron feeler gauge. After drying at 120.degree. C. for 5
minutes, the transfer film was laminated and layered on 50 micron
polyester film to an adhesive thickness of 250 microns for
compliance testing.
[0057] The adhesive of Example 2 was also characterized by
compliance according to the TA Peak Force methodology described
herein, yielding a peak force of 86 grams, and a percent loss of
58%.
[0058] An experiment was carried out on ten voluntary test subjects
to measure the pain experienced upon removal of certain tapes to
which an adhesive was applied. Several types of comparative
commercial medical adhesives were used along with a tape using the
adhesive formulated in accordance with Example 2. One commercial
sample was a Tegaderm.RTM. negative pressure would therapy drape
(an approximately 20 micron acrylic PSA on 25 micron polyurethane
film commercially available from 3M) and another was a dressing
made using an approximately 250 micron layer of a silicone gel
adhesive (commercially available as Dow Corning Soft Skin 9850) on
a 30 micron polyurethane film. The silicone gel adhesive, when
coated at a thickness of 25-50 microns, has very low adhesion and
tends to fall off. In order to increase the adhesion, commercial
silicone adhesives are generally coated at greater thicknesses, and
the silicone adhesive used as a comparative example in the
experiments was applied to the manufacturer's recommended coating
thickness of 250 microns.
[0059] The adhesive of Example 2 was coated to a thickness of
approximately 50 microns and applied to a 30 micron polyurethane
film.
[0060] Each of these samples was applied to each test subject's
forearm and left in place for 24 hours. The samples were peeled
back at an angle of 90.degree. and the peel speed was 12
inches/minute in a tensile tester. The pain level was evaluated
using the Wong-Baker pain scale. The amount of skin cells remaining
on the adhesive after peeling from the forearm was also evaluated
and graded according to the 0-5 scale reflected in Table 2
below.
TABLE-US-00002 TABLE 2 Assessment Scale Description 0 Few visible
skin cells, <1% patch area 1 Some visible skin cells, <10%
patch area 2 Moderate visible skin cells, <50% patch area 3
Nearly full coating of skin cells, still some tack to PSA 4 Full
coating of skin cells, no tack to PSA 5 Full coating of skin cells
and body hair with visible removal of skin from forearm of body
[0061] The results of the experiment are reflected in Table 3:
TABLE-US-00003 TABLE 3 Tegaderm .RTM. Dow Corning Example 2
negative pressure Soft skin 9850 on on 30 micron wound therapy 30
micron polyurethane drape polyurethane film film Pain Ranking 4.1 0
0.9 Peel (N/cm) 0.90 0.33* 0.95 Skin Cell 3.8 0.1 0.1 Assessment
(0-5) Edge Lift (% 0% 50% 0% area) *The silicone adhesive fell off
in 50% of the test subjects within 24 hrs of application and these
were not counted in the peel average.
[0062] The MVTR for each of the three adhesives was measured using
the upright Payne cup method at 20% RH and 37.degree. C. The
results of the MVTR experiment are shown below in Table 4.
TABLE-US-00004 TABLE 4 Tegaderm .RTM. Dow Corning negative pressure
Soft skin 9850 on Example 2 wound therapy 30 micron on 30 micron
drape polyurethane film polyurethane film MVTR 636 321 1280
(g/m.sup.2-day)
[0063] The effect of gamma sterilization is determined by the
change in peel adhesion value before and after treatment. It is
desired that little or no change occur after treatment which
signifies that the adhesive is resistant to the treatment. If the
peel value changes then the performance of the adhesive in the
final product cannot be predicted reliably. To compensate for this
change in performance in conventional adhesives the formulators
often error on the aggressive side and hope that the adhesive
returns within a workable performance range after gamma
sterilization. This leads to product variability and can result in
a quality control issue, a manufacturing nightmare. Furthermore,
the gamma treatment process itself cannot be controlled precisely.
The gamma treatment dose for the medical industry varies from 25 to
40 kGy which makes controlling the adhesive performance even more
troublesome. The effect of the gamma sterilization experiment on
peels is shown below in Table 5, with the performance of the
adhesive of Example 2 formulated in accordance with exemplary
embodiments of the invention shows that the adhesive remains stable
when subjected to gamma treatment.
TABLE-US-00005 TABLE 5 Dow Example 2 Medical grade Corning Soft
skin on 30 micron Acrylic 9850 on 30 micron polyurethane adhesive
polyurethane film film Peel before gamma 208.7 30.1 84.8 treatment
(g/cm) Peel after ~25 kGy 60.3 Could not be 97.1 gamma treatment
measured (g/cm)
[0064] While the invention has been described with reference to
particular embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended claims and
all other patentable subject matter contained herein.
* * * * *